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Building a Backend Application with Go

Middleware Creation for GraphQL

Learn how to create a middleware for the GraphQL application.

We'll cover the following...

Add a middleware

Before creating a middleware, we create some additional helpers in the auth.go file. These helpers verify the JWT token.

We add a helper function called ExtractTokenMetadata inside auth.go in the utils directory.

Go (1.18.2)
package utils
import (
    "net/http"
    "strconv"
    "strings"
    "time"
    "github.com/golang-jwt/jwt/v4"
)
// TokenMetadata represents JWT token metadata
type TokenMetadata struct {
    Expires int64
    UserId  string
}
// ExtractTokenMetadata extracts JWT token metadata
func ExtractTokenMetadata(r *http.Request) (*TokenMetadata, error) {
    // verify the JWT token
    token, err := verifyToken(r)
    // if verification is failed, return an error
    if err != nil {
        return nil, err
    }
    // get a JWT claim from the JWT token
    claims, ok := token.Claims.(jwt.MapClaims)
    // check if the token is valid
    var isValid bool = ok && token.Valid
    // if the JWT token is valid, return the JWT token metadata
    if isValid {
        // set token expiration
        expires := int64(claims["exp"].(float64))
        // set user ID for the token
        userId := claims["userId"].(string)
        // return the JWT token metadata
        return &TokenMetadata{
            Expires: expires,
            UserId:  userId,
        }, nil
    }
    // return an error
    return nil, err
}
Function to extract the JWT token metadata

Below is an explanation of the code above:

  • In lines 13-16, the TokenMetadata struct is created to store the JWT token metadata.

  • In line 21, the JWT token is verified.

  • In line 29, the claim of the JWT is extracted.

  • In line 32, the JWT token is validated.

  • In line 35, the JWT token is checked to ensure the token is valid.

  • In line 37, the JWT ...